In general, in a liquid crystal display device configured to perform color display, one pixel is divided into three subpixels of a red pixel provided with a color filter that transmits red light, a green pixel provided with a color filter that transmits green light, and a blue pixel provided with a color filter that transmits blue light. While the color filters provided in these three subpixels enable the color display, about ⅔ of a backlight beam with which a liquid crystal panel is irradiated is absorbed in the color filters. This poses a problem that light utilization efficiency is low in the liquid crystal display device employing the color filter system. Consequently, attention has been focused on a liquid crystal display device employing a field sequential system configured to perform the color display without using the color filters.
In the liquid crystal display device employing the field sequential system, one frame period, which is a display period of one screen, is typically divided into three fields. While the field is also called a sub-frame, in the following description, the term of “field” is consistently used. For example, one frame period is divided into a field (a red field) configured to display a red screen based on a red component of an input image signal, a field (a green field) configured to display a green screen based on a green component of the input image signal, and a field (a blue field) configured to display a blue screen based on a blue component of the input image signal. The primary colors are displayed one by one as described above, by which a color image is displayed in a liquid crystal panel. Since the display of the color image is performed in this manner, the color filter is not required for the liquid crystal display device employing the field sequential system. Thus, the light utilization efficiency in the liquid crystal display device employing the field sequential system is about three times as high as that of the liquid crystal display device employing the color filter system. Accordingly, the liquid crystal display device employing the field sequential system is suitable for increase in luminance and decrease in power consumption.
In a general liquid crystal display device, the one frame period is 1/60 second. Accordingly, in the case where the one frame period is divided into three fields as described above, a length of each of the fields is 1/180 second. That is, a refresh rate indicating a speed of rewriting the whole screen displayed in the liquid crystal panel is 180 Hz.
In some cases, a signal processing circuit configured to apply signal processing to an input image signal, and a timing control circuit configured to control operation of a gate driver (a scanning signal line drive circuit), a source driver (a video signal line drive circuit) and the like are provided in different substrates. In such a configuration, in order to implement the refresh rate of 180 Hz, it is necessary that data transfer is performed at a frequency of 180 Hz between the substrates.
Moreover, as to the liquid crystal display device employing the field sequential system, conventionally, there has been known a problem that color breakup occurs. Consequently, in order to suppress the occurrence of the color breakup, the one frame period may be divided into four or five fields. In this case, in the one frame period, in addition to the red field, the green field, and the blue field, for example, a white field, a yellow field, and the like are provided. In a case where one frame period is divided into four fields, the refresh rate is 240 Hz. In the configuration where the signal processing circuit and the timing control circuit are provided indifferent substrates, the data transfer needs to be performed at a frequency of 240 Hz between the substrates. In a case where one frame period is divided into five fields, the refresh rate is 300 Hz. In the configuration where the signal processing circuit and the timing control circuit are provided in different substrates, the data transfer needs to be performed at a frequency of 300 Hz between the substrates.
As described above, when the field sequential system is employed, the data transfer between the substrates needs to be performed at a high frequency. As means for implementing the data transfer at the above-described high frequency, it can be considered to use a special interface. However, the use of the special interface increases costs. Consequently, in order to perform the data transfer at a high frequency, there has been proposed a technique of using a well-known standardized interface such as HDMI (registered trademark) (High-Definition Multimedia Interface), DVI (Digital Visual Interface) and the like. It should be noted that the DVI is a standard of a video output interface designed to make the most use of video quality of a digital display device. A standard resulting from adding various functions to the DVI is the HDMI.
It should be noted that, in relation to the present invention, the following prior art document has been known. Japanese Laid-Open Patent Publication No. 2001-331142 discloses an invention of an image display device in which a multi-gradation video signal is converted to a pulse width modulation signal for each bit of gradation data to drive a display element in a time-division manner for each bit. According to this image display device, since an existing pulse width modulation (PWM) circuit can be used, an increase in circuit scale can be suppressed.